It has been shown, that in patients with very severe chronic obstructive pulmonary disease (COPD) the additional use of non-invasive ventilation during pulmonary rehabilitation (PR) may enhance the benefits of PR. It is assumed that the non-invasive ventilation techniques provides a better recovery of the respiratory pump during the night. If non-invasive ventilation also decreases the metabolic demands during night is unknown and is aim of this study. During a 3 week inpatient pulmonary rehabilitation program a total of 85 patients with chronic obstructive pulmonary disease stage IV will be recruited for this study. There will be a 4:1 distribution into 2 groups. 68 patients with an indication for the use of a non-invasive ventilation will be involved in the intervention group where non-invasive ventilation will be initialized. 17 patients with chronic obstructive pulmonary disease stage IV without an indication for the use of non-invasive ventilation will be involved in a control group to detect the changes in nocturnal energy expenditure produced by pulmonary rehabilitation alone. All outcome measurements will be performed during day 1-3 and will be repeated after 12 days (with or without non-invasive ventilation) at day 15-17 of the pulmonary rehabilitation program.

A sub-trial of this study is to validate night movement accuracy of the Dynaport activity monitor with the observations made by a night-vision camera in the sleep lab. This will be performed in study participants as well as in healthy volunteers.

Inclusion Criteria for Intervention group:

• chronic obstructive pulmonary disease stage IV
• indication for the use of a nocturnal non-invasive ventilation (according to the German guidelines Schoenhofer et al. 2008)
• patient has not yet used non-invasive ventilation at all or inadequately (less than 3 hours per day)

Exclusion Criteria for Intervention group:

• acute exacerbation of chronic obstructive pulmonary disease
• severe heart failure
• body-mass-index >35 m²/kg
• fever

Inclusion Criteria for control group:

• chronic obstructive pulmonary disease stage IV (- healthy volunteers are also eligible for the sub-trial of this study to validate night movement accuracy of an activity monitor)

Exclusion Criteria for control group:

• acute exacerbation of chronic obstructive pulmonary disease
• indication for the use of a non-invasive ventilation
• severe heart failure
• body-mass-index >35 m²/kg
• fever